In a conventional wireless communication environment, a signal sent by a transmitter usually reflects off various objects in the environment, and takes several paths before reaching the receiver. This phenomenon, called multipath propagation, causes the same signal to arrive at the receiver at different times. The multipath propagated signals received tend to overlap and lead to inter-symbol interference (ISI) problems. The phase difference between the received signals may cause the signals to cancel each other, resulting in low power level and poor signal quality at the receiver.
The variation of received amplitude and phase is referred to as fading. Traditionally, receiver systems are designed to mitigate the fading problem by using diversity receivers that have several receiver paths, where the receiver circuitry selects among the receiver paths that provide the strongest received signal. Diversity receivers, while effective for reducing fading, are more expensive compared to receivers without diversity.
In some systems, such as an ultra-wideband (UWB) system, the fading problem is less pronounced due to the nature of the signal. UWB technology is used in wireless communication systems for transmitting and receiving data over a wide spectrum. A UWB signal is commonly treated as a short radio frequency (RF) signal. Since the signal is short (often on the order of a few nanoseconds), the multipath propagated signals received do not significantly overlap with each other. It would be useful to take advantage of this characteristic of the UWB system to design receivers that would capture more energy from the received signals. It would also be desirable to have receiver designs that are cheaper to implement, without using diversity receivers.